1. Field of the Invention
This invention relates to the field of mass storage systems. In particular, the invention relates to the management of storage transactions in, and the configuration of, intelligent storage area networks for the purposes of allocating and changing the allocation of storage resources.
2. Description of the Related Art
The storage of large amounts of data in so-called mass storage systems is becoming a common practice. Mass storage systems typically include storage devices coupled to file servers on data networks. Users in the network communicate with the file servers for access to the data. The file servers are typically connected to specific storage devices via data channels. The data channels are usually implemented with point-to-point communication protocols designed for managing storage transactions.
As the amount of storage increases, and the number of file servers in communication networks grows, the concept of a storage area network (SAN) has arisen. Storage area networks connect a number of mass storage systems in a communication network which is optimized for storage transactions. For example, Fibre Channel arbitrated loop (FC-AL) networks are being implemented as SANs. The SANs support many point-to-point communication sessions between users of the storage systems and the specific storage systems on the SAN.
File servers and other users of the storage systems are configured to communicate with specific storage media. As the storage systems expand or media is replaced in the system, re-configuration is required at the file servers and other users. Also, if a need arises to move a data set from one device to another, in a so-called data migration operation, it is often necessary to block access to the data set during the migration process. After migration is complete, re-configuration at the user system must be executed to make the data available from the new device. The blocking of access to the data set during the transfer is a particularly costly action for large data sets having many users. Both the amount of time required to move a copy of the data to the new device, and the number of people inconvenienced can be very large. The above identified related application entitled Method And System For Managing Data Migration For a Storage System, describes solutions to many of the problems associated with migrating data sets among devices in a storage network.
Also, failures of devices in the storage network can occur. Upon failure of a device in an array, data is lost or performance suffers while the data on the failed device is reconstructed. When failure occurs, replacement devices may be needed to recover network performance. The insertion of replacement devices requires data migration operations from backup systems, or from redundant storage in the network. Thus, device failures cause additional problems for network administration.
Data sets are stored in sets that include arrays of storage devices in order to improve the performance of data storage transactions, and to improve fault tolerance in data storage systems. Common configurations for arrays of storage devices are known as RAID levels. For example, RAID 0 consists of a striped Disk Array. The data in a RAID 0 array is broken down into data sets referred to as blocks, and each block is written on a separate disk drive or storage device. RAID 1 consists of mirrored and duplexed sets of storage devices. RAID 3 consists of a set of storage devices on which data blocks are subdivided into stripes, which are written on multiple storage devices. In addition, stripe parity is generated on writes and stored within the array for each striped data block, and checked during reads of the data. In a RAID 5 arrays, data blocks are written on the disks within the array, and parity for the blocks of the same rank is generated on writes. The block parity is recorded in distributed locations within array, and checked during reads. A variety of other RAID levels are well-known. Recovery from failures of storage devices involved in RAID configurations, or in other sets of storage arrays used to store a data set, involves a variety of mechanisms and procedures which can make administration of a storage system complex.
Modern storage devices, such as hard disk drives, are extremely reliable, with a typical mean time between failure rating of 300,000 hours or more. However, as the number of disk drives per system increases with storage area network technology, and the size of the typical disk drive grows, administrators will experience failures of even very reliable devices. Thus, technology is being developed to elevate the protection of user data. For example, systems have been designed for self-monitoring analysis and reporting in disk drives. For example, the so-called S.M.A.R.T. system developed by Compaq Computer provides for disk drives and other storage devices to generate signals that communicate their predicted reliability status to users and system administrators. With this information, an administrator is able to prevent system downtime, productivity loss and even the loss of valuable data if appropriate corrective action is taken. Other utilities have also been developed for the purposes of diagnosing storage device reliability status.
Overall, as the complexity and size of storage systems and networks increase, the problems of managing failed or worn out storage devices along with configuration of the users of the data and of the storage systems themselves multiply. Accordingly, there is a need for systems that simplify the management of storage systems, and in particular the management of data in devices that need to be replaced, while taking advantage of the flexibility and power of the SAN architecture.
The present invention provides a method and an apparatus for use in a storage network that facilitates the protection of data in, and replacement of, storage devices that are about to fail before the failure happens. In a network that includes a plurality of sets of storage devices which store respective data sets, a storage device about to fail in one set can be replaced by another storage device from another set of storage devices which is being used to store data having a lower priority. In this manner, the integrity of the higher priority data is maintained, and storage devices that are about to fail are migrated into lower priority storage device sets.
The method comprises assigning priorities to sets of storage devices which store respective data sets in the network. In addition, the method includes detecting a condition of a first particular storage device in a particular set of storage devices that has a first priority. According to various embodiments, conditions which are detected are those which indicate that the first particular storage device is suffering events which make it likely to fail, or otherwise suffering from reduced performance. The conditions are detected for example, by the receipt of a signal from the storage device itself, or by the monitoring of statistics concerning the performance of the storage device. The method of the present invention further provides for selecting a second particular storage device in a second particular set of storage devices having a second priority, which can be used in place of the first particular storage device. In response to detecting the condition, the data set stored in the first particular storage device is migrated to the second particular storage device, and the second particular storage device is identified as a member of the first particular set. The first particular storage device can be gracefully removed from the network, while only affecting the performance of the data access in the lower priority second particular set of storage devices.
According to another aspect of the invention, embodiments are provided in which the method includes determining whether a spare device is available for use in the first particular set of storage devices, and if a spare device is not available, then migrating the data set to the second particular storage device.
According to one embodiment of the invention, the step of migrating the data set includes transferring copies of blocks of data in the data set from the first particular storage device to the second particular storage device via an intermediate device, and the transferring includes:
(i) setting a parameter indicating the size and location of the data set stored in the first particular storage device;
(ii) generating a request to copy a block from the data set to a buffer in the intermediate device;
(iii) generating a request to transfer the block from the buffer to the second device;
(iv) setting a parameter indicating blocks from the data set stored in the second device; and
(v) repeating the steps (ii) through (iv), until a copy of the data set is stored in the second device.
In one embodiment of the invention, the method includes fulfilling the data access requests through the intermediate device.
In another embodiment of the method, the step of migrating the data set comprises a background process executed without blocking data access requests from the client.
In one embodiment, an intermediate device for the storage network is provided. The intermediate device comprises a plurality of communication interfaces, adapted for communication with a plurality of sets of storage devices storing a corresponding plurality of data sets, and for communication with one or more clients issuing data access requests for access to the plurality of data sets. Data transfer resources are coupled to the plurality of communication interfaces, and transfer data access requests identifying a particular data set among the plurality of communication interfaces. A logic engine is provided which identifies members of the plurality of sets of storage devices, and in response to detection of a condition of a first particular storage device in a first particular set of storage devices having a first priority, migrates the data set stored in the first particular storage device to a second particular storage device having a second priority, and thereafter identifies the second particular storage device as a member of the first particular set of storage devices.
According to various embodiments of the invention, the logic engine comprises data structures that store information, such as status information, information identifying the data set, and other data concerning the transfer. In one embodiment, the intermediate device stores a parameter indicating an extent of the data set which is already copied to the second storage device.
According to other aspects of the invention, the data transfer resources include logic operable during the transfer of the data set which direct data access requests to the first and second particular storage devices in response to a type of data access request, and a status of the transfer. In one embodiment, when the data access request comprises a request to write data in the data set, the data transfer resources direct the data access request to both the first and second storage devices if the request identifies data already copied to the second device. In another embodiment, when the data access request comprises a request to read data in the data set, the data transfer resources include logic to direct the data access request to one or both of the first and second storage devices.
According to other embodiments of the invention, the data transfer resources comprise a plurality of driver modules, and configurable logic linking driver modules into data paths, so that data paths include respective sets of driver modules. The plurality of driver modules includes one or more hardware driver modules for management of communication interfaces, and one or more internal driver modules to perform data path tasks independently of the plurality of communication interfaces.
According to yet another embodiment, the present invention provides a storage server having sophisticated data processing resources for the purposes of controlling the routing of data storage transactions, and the migration of data sets among a pool of storage devices. The data processing resources comprise a plurality of driver modules and configurable logic linking driver modules into data paths. Each configured data path acts as a virtual circuit that includes a set of driver modules selected from the plurality of driver modules. A data storage transaction which is received at a communication interface is mapped to one of the configured data paths according to the initiating host and according to the logical address of the storage extent subject of the transaction. Upon completion of a process used to migrate the data set as described above, the configuration of the data path is changed to direct the session including the transaction to the new location of the data.
The data paths configured in this manner act as virtual storage devices, facilitating the reassignment of physical storage devices among data sets according to a priority. Users of the data communicate with a communication interface on the storage server according to a protocol for a particular storage device. Inside the server, the transactions according to that protocol are mapped to a virtual storage device implemented by sets of drivers. Setting up and changing the storage tasks performed in a particular data path, and setting up and changing the mapping of a storage extent from one data path to another, and assigning storage devices to sets of storage devices are accomplished by configuring the sets of driver modules within the storage server.
The present invention provides an intelligent storage routing device which manages logical and physical access to a pool of shared storage devices, reassignment of physical storage according to data priority, and transfer of data sets among the storage devices without blocking access to the data sets. The device is logically closer to the client server than to the storage devices, and responds to client specific requests for storage transactions which require accessing and sharing a storage area network coupled to the device. The device manages the use of a cache memory to enhance performance. Very large data sets, on the order of many terabytes in size or more, can be transferred from old to new storage devices, or vice versa, as the storage resources in a network change, without blocking access to the data sets.
Other aspects and advantages of the present invention can be seen upon review of the figures, the detailed description and the claims which follow.